Last week, India expelled Pakistani diplomat Mahmood Akhtar from the embassy in New Delhi after detaining him on espionage charges. Within hours, Islamabad retaliated by expelling Indian diplomat Sujeel Singh.

Mr Akhtar said he was arrested by Indian police while visiting the zoo in New Delhi. He added that while in detention he was tortured and beaten, and forced to confess on camera to working for Pakistan's spy agency, the Inter-Services Intelligence.

India has issued no comment over the claims.

The diplomatic spat has grown out of rising violence in Kashmir, a mountainous region claimed by both countries and divided into Pakistani and Indian-controlled regions.

Several troops from both sides have died in recent skirmishes along the Line of Control, which demarcates the two parts of Kashmir.

A number of militant attacks in Indian-controlled Kashmir have added to the tension.

Two of the three wars between India and Pakistan since 1947 have been fought over their competing claims to Kashmir.